Compounds that exhibit high-affinity binding to voltage-dependent calcium channel subunit α2δ have been shown to be effective for treating, for example, neuropathic pain (see e.g., Non Patent Literatures 1 and 2). In this context, neuropathic pain refers to chronic pain caused by nervous tissue injury or the like and is a disease that significantly impairs the quality of life in such a way that patients suffer from depression due to severe pain attacks.
Several types of α2δ ligands are currently known as therapeutic drugs for such neuropathic pain. Examples of α2δ ligands include gabapentine and pregabalin. α2δ ligands such as these compounds are useful for treating epilepsy and neuropathic pain or the like (e.g., Patent Literature 1).
However, it has been reported that, for example, for gabapentine, its efficacy in the treatment of postherpetic neuralgia is approximately 60% according to patients' own evaluation (see e.g., Non Patent Literature 3) and that for pregabalin, its efficacy in the treatment of painful diabetic neuropathy is approximately 50% according to patients' own evaluation (see e.g., Non Patent Literature 4).
Other compounds are disclosed in, for example, Patent Literatures 2, 3, and 4.